Double diaphragm loud-speaker



March 2@, 1945. K 2,371,951

DOUBLE DIAPHRAGM LOUDSPEAKER Filed Jan. '7, 1943 Inventor: El lsworth D. Cook,

His Attorney.

man Mar; 20. 1945 nouann nurnnscu noun-scum V Ellsworth D. Oook, Scotla, N. Y,., aslgnor to General Electric York Company, a corporation of New Application January '1, 194:, as. n. 411,515 2 Claims. (01. ire- 155) My invention relates to acoustic devices of'the dynamic type for transmitting signals over both low and high' ranges'of frequencies, particularly to loudspeaker or like devices employing two diaphragms of different size and characteristic for respectively transmitting a low and a high frequency range, and itsprinclpal object is to provide an improved acoustic device ofthe two-diara typ It is well known from experience with developments in the acoustic prior art involving various forms of'dia'phragms, particularly the large diameter cone diaphragms employed in dynamic loudspeakers, that it is diflicult practically, even if not impossible theoretically, so to construct a single diaphragm that it may be forced satisfactorily to-operate over an extremely extended frequency range, such a range for example as one comprising both the high frequency portion and the low frequency portion of the voice range.

At least part of the difliculty i to be found in the excessive'mass' loads imposed at the high frequencies on the voice coil. The loads imposed arepractically prohibitive at high frequencies if it be attempted so to construct the large diameter diaphragm structure which is capable of moving integrally as a piston at low frequencies and especially adapted to transmission of these low frequencies, that it will also be capable of transmitting the high frequencies while moving as a piston. The practical result of this difllcultv when employing the single diaphragm is that a certain amount of elasticity in the diaphragm, avoiding the piston action of the diaphragm as a unit at the high frequencies, is usually unavoidable, it being thusfound necessary to permit wave action in the diaphragm in order to transmit the high frequencies at all adequately without excessive loading of the driving coil.

It is a further and particular object of my present invention to provide an'improved two-diaphragm'acoustic device wherein loading of the driving winding by the mass of the low frequency diaphragm system at the high frequency range of operation is prevented.

. acterlstic of my invention are set forth with parthat of conventionalforms. and an inverted diaphragm of-general cone shape and of approximately' the diameter of the voice coil i rigidly attached thereto. A relatively large diameter cone diaphragm which is of usual form is also connected to the voice coil, but the connection to this large diaphragm is through an elastic coupling. The mass of the cone structure comprising the large diaphragm, and theela'sticity of its coupling to the-voice coil, are so proportioned and arranged that the vibratory mechanical system constituted by the large cone structure is adjusted to respond to the vibratory energy supplied by the voice coil over only the desired low frequency portion of the voice range.

The novel features which are considered charticularly in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing, the single figure of which is a cross-sectional fragmentary view of an acoustic device in which my invention has been embodied.

Referring to the single figureof the drawin 'the acoustic device which is shown therein for In accordance with my present invention the above noted diillculties are overcome and the above noted and other objects attained by the provision of a double diaphragm device of special arrangement, but which in appearance is not extremely dissimilar to the conventional form of cone diaphragm loudspeaker. In an acoustfc device in accordance with the invention, the diameter of the operating winding or voice coil vided with suitable suspension means, compris ing a usual flexible ring H which may be secured to a fixed frame element (not shown). A second diaphragm I2 is provided which is of substantially less diameter than that of the diaphragm III, of the order of one-half, for example, and which is mounted in inverted relation with. the latter diaphragm at the smaller end thereof. The diaphragm i2 is fitted like a cap adjacent the outer side of a voice coil'l3 and extending within the larger diaphragm. The diaphragm I2 is of a general cone shape, but while it may be a cone as illustrated, it may also be of somewhat differentinverted positioning of the smaller diaphragm it, whatever be its exact form, resides in the fact that the inverted diaphragm spreads the for the diaphragm is increased somewhat over high frequencies overs somewhat wider solid angle than would be obtained with the conventional placing of a cone diaphragm.

For driving the two diaphragms in and |z,.

the diameter of the smaller diaphragm H.

The smaller diaphragm I2 is so mounted as to be driven or vibrated directly by the voice coil as by securing the edge it of the latter diaphragm rigidly to the outer end I! of the coil support H. The larger diaphragm Ill, however, is not arranged to be driven or vibrated directly by the voice coil it but through an elastic coupling. For this purpose the coil I3 and diaphragm ID are preferably operatively associated with each other by means of an elastance elemental) which may be in the form of a ring of pliant material, the sides II and 22 of which are secured respectively to the voice coil support I and to the smaller edge 23 of the diaphragm III, and which comprises a fold of Sylphon bellowsiike form 24.

To provide suitably larger diameter mounting space for the voice coil i! which is preferably of considerably larger diameter than in usual praciice, the inner coreor pole piece I! of the magnet system may be provided with an extension piece N of larger diameter, and the central opening in the outer pole piece l8 may be of correspondingly larger diameter to provide the required larger diameter air gap ll.

In operation of the acoustic device illustrated 'in the drawing, assuming that the device is operating in the high frequency portion of the voice range, then since the broadly tuned mechanical vibratory system, constituted by the coupling elastance 24 and the mass of the cone structure comprising the larger cone i0, responds only over the predetermined low frequency portion of the voice range, all of the high frequency portion of the range is'therefore transmitted only from the smaller diaphragm [2. When on the other hand the device is operating in the low frequency portion of the range, although the smaller diaphragm I! then vibrates together with the larger diaphragm Ill being rigidly secured at all times to the veil coil, nevertheless the larger diaphragm i responds to and transmits substantially all of this low frequency portion of the voice range.

Therefore in operation of the. acoustic device embodying my invention, the mass of the low frequency system including the larger cone Ilia prevented from becoming a load on the voice coil II .when the acoustic device is operating on the high frequency portion of the voice range. This mass, it will be noted,would become a load on the voice coil if the mass were vibrated over the entire frequency range of the device, and would necessitate either a driving system of much higher power at the high frequencies or might even under the above assumption refuse to vibrate in the as of the order for example of one-half that of of diaphragm Ill. It will be understood, however, that the diameter of diaphragm I! while not especially critical should be such in any case that this diaphragm may have sufficient total radiation resistance to radiate the full amountof high frequency energy required. Otherwise stated, it

is therefore the maximum value of this high frequency energy which is a factor in determining the dimensions of the high frequency diaphragm. My invention has been described herein in a particular embodiment for purposes of illustraof said diaphragm, said cone-shaped diaphragm having a smaller diameter approximately onehalf its larger diameter, an inverted diaphragm of approximately the same diameter as said wind ing connected thereto for transmitting'a maximum amount of energy at a relatively high range of frequencies, and elastance means connecting said winding to said first-named diaphragm for preventing the mass of said first named diaphragm from leading said winding at said high frequency. V v

2. In combination, in a dynamic type loudspeaker, a truncated cone-shaped diaphragm of relatively large diameter for transmitting a relatively low range offrequencies, an operatin winding approximately one-half the larger diameter of said diaphragm, said cone-shaped diaphragm having' a smaller diameter approximately one-half its larger diameter, an inverted diaphragm of approximately the same diameter as said winding connected thereto for transmitting a maximum amount of energy at a relatively high range of frequencies, and a bellows-like elastance element connecting said winding. and said first-named diaphragm for preventing the mass of said first-named diaphragm from loading said winding at said high frequency range. said element being constructed and arranged to transmit substantially all the low frequency energy passing from said winding'to said first diaphragm along paths parallel to the central axis of said first diaphragm.

ELLSWORTH D. COOK. 

